1. Field of the Invention
The present invention relates to a high-frequency switch, or more particularly, to a high-frequency switch employed in a communication equipment to be installed in a base station for telephony using digital portable telephones or personal handy phones (PHSs).
2. Description of the Related Art
In recent years, the importance of a shared antenna switch has attracted attention along with the prevalence of digital mobile communication equipment employed in a base station or the like for telephony using digital portable telephones or PHSs. The shared antenna switch selectively connects a plurality of antennas by controlling switch selection.
As the shared antenna switch, a high-frequency multi-branch switch using pin diodes or high-frequency relays is used in general. Not only a requirement for a compact design and a high performance but various other requirements have been made for the high-frequency multi-branch switch. Specifically, it is required required improve a distortion characteristic relative to a high output, minimize a loss, achieve highly efficient isolation, and reduce the cost for the purpose of coping with a multi-branch switch configuration for meeting the demand for an increase in the number of transmission/reception channels at a mobile communication base station and in transmission power and with an antenna switching diversity system.
When a high-output power amplifier is connected to a conventional high-frequency multi-branch switch, the problems below occur.
When high-frequency relays that are mechanical switches are used for a high-frequency multi-branch switch, high performance is ensured in terms of the abilities to withstand high power, suppress distortion, minimize a loss, and achieve highly efficient isolation. However, there arise problems that the circuit scale (shape) becomes large and the switching speed of the switch is low.
When pin diodes are used for a high-frequency multi-branch switch, a pin diode designed for high output power is included. A parasitic capacitance in the pin diode cannot be ignored from the viewpoint of the flow of a high-frequency current. This poses a problem that isolation efficiency deteriorates and insertion loss increases.